1. Field of the Invention
The present invention relates to a hydraulic press of the type containing a pressure cell with a diaphragm of flexible material and a pad, influenced by said diaphragm, which is also of a flexible material, said press pressing workpieces against a tool and giving them the desired shape. A press of this kind has normally a very large working surface and is used, for example, in the manufacture of sheet-metal parts in the aviation industry, for example ribs and beams of various kinds.
2. The Prior Art
A press according to the invention comprises a press stand with a working space with a substantially rectangular cross-section. In this the pressure cell and the pad are normally suspended from the roof of the working space. Workpieces are placed on tools on a trough-shaped carrying member, which together with the workpieces is pushed into the working space of the press so that it will be located below the pressure cell and the forming pad. The pressure cell contains a bag-like diaphragm which is shaped with an annular bead around the opening. The diaphragm is clamped between two disc-shaped attachment members, one of these being located inside the bag-like diaphragm. The discs form an annular groove adjusted to the bead, which groove fixes the position of the diaphragm. The cavity in the pressure cell is thus defined by the inner surface of the diaphragm and of the inner surface of the disc which is located inside the bag-like diaphragm. The connection between the diaphragm bead and the inner disc-shaped attachment member must be made so that a perfect seal is obtained. The bead has usually been glued or vulcanized onto the inner attachment member and clamped between the two attachment members which form the groove for the bead, but it has been found that pressure medium tends to leak out between the bead and the inner attachment member. The difficulties in obtaining sealing have increased when the working pressure increases. Today the working pressure in modern presses is of the order of magnitude of 1000 bar, but users desire presses which permit higher working pressures.